1. Field of the Invention
The present invention relates to a semiconductor device constituted by thin film transistors (TFT) formed on a substrate having an insulating surface and a method of manufacturing the same. Such a semiconductor device includes an IC, an LSI, an electrooptical device and the like, and especially it is effective to apply the present invention to the electrooptical device.
2. Description of the Related Art
In recent years, research in a semiconductor device constituted by TFTs using polycrystalline silicon thin films (polysilicon film: p-Si film) instead of TFTs using noncrystalline silicon thin films (amorphous silicon film: a-Si film), is developed. Especially, development and research in an active matrix type display device in which semiconductor devices are integrated on a substrate, is remarkable, since the demand as a display device of a PC monitor, a video camera, a projection or the like has been increased.
As such an active matrix type display device, there is known one disclosed in U.S. Pat. No. 5,250,931 (Misawa et al.). However, additional values are recently required, and there has been proposed an SOP (System On Panel) plan in which a logic circuit (signal processing circuit such as a display control circuit and an arithmetic circuit), which are conventionally realized by an externally equipped IC, is mounted on the same substrate by TFTs.
Also, research for manufacturing a conventional IC or VLSI itself by TFTs, is made to proceed. It is because a TFT is formed on an insulating substrate so that it has a feature that parasitic capacitance is extremely small, and it can be said that the TFT is more effective in high speed operation than an FET formed on single crystal silicon.
However, a technique for forming a TFT which is capable of realizing the plan has not been established. The reason is that when a presently used polysilicon film (including a so-called high temperature polysilicon and low temperature polysilicon film) is employed, it is difficult to obtain a TFT having enough performance to constitute a circuit requiring high frequency driving.
Although the improvement of an operation speed of a TFT can be made for the time being by decreasing the size of the TFT, the reduction of the channel length (or gate length) results in the short channel effect, so that disadvantages such as lowering of a drain withstand voltage is caused. Thus, in the TFT using a conventional silicon thin film, the improvement of an operation speed by the scaling law reaches the limits, and it is difficult to increase the operation speed any more in view of reliability. Further, the silicon thin film has a problem that crystal grains and crystal grain boundaries exist irregularly, and the crystal grain boundaries greatly influence the TFT characteristics to cause irregularity.
An object of the present invention is to overcome the above described problems to provide a semiconductor device constituted by TFTs formed on a substrate having an insulating surface, and a method of manufacturing the same. Especially, an object of the present invention is to provide an electrooptical device (hereinafter referred to as a system display) carrying a logic circuit constituted by TFTs and functionally systematized, and a method of manufacturing the same.
Incidentally, the semiconductor device includes all devices using a semiconductor to function, and all of an IGFET, a TFT, an IC, an electrooptical device and an applied product thereof are included in the category of the semiconductor device in a wide sense.
According to an aspect of the present invention, in an electrooptical device constituted by disposing a pixel matrix circuit, a driver circuit and a logic circuit on the same substrate, the pixel matrix circuit, the direr circuit and the logic circuit include a plurality of TFTs each having an active layer of a crystalline silicon film and a subthreshold coefficient of 60 to 100 mV/decade, and channel formation regions of the plurality of TFTs included in the respective circuits are made of lateral growth regions having growth distances different from each other according to characteristics required by the respective circuits.
According to another aspect of the present invention, in an electrooptical device constituted by disposing a pixel matrix circuit, a driver circuit and a logic circuit on the same substrate, the pixel matrix circuit, the direr circuit and the logic circuit includes a plurality of TFTs each having an active layer of a crystalline silicon film and a subthreshold coefficient of 60 to 100 mV/decade, channel formation regions of the plurality of TFTs included in the respective circuits are made of lateral growth regions having growth distances different from each other according to characteristics required by the respective circuits, and the growth distances of the lateral growth regions which become the channel formation regions of the TFTs constituting the logic circuit and/or the driver circuit, are shorter than the growth distances of the lateral growth regions which become the channel formation regions of the TFTs constituting the pixel matrix circuit.
According to still another aspect of the present invention, in an electrooptical device constituted by disposing a pixel matrix circuit, a driver circuit and a logic circuit on the same substrate, the pixel matrix circuit, the direr circuit and the logic circuit include a plurality of TFTs each having an active layer of a crystalline silicon film and a subthreshold coefficient of 60 to 100 mV/decade, channel formation regions of the plurality of TFTs included in the respective circuits are made of lateral growth regions having growth distances different from each other according to characteristics required by the respective circuit, and channel lengths of the plurality of TFTs correlates with the growth distances of the lateral growth regions.
According to still another aspect of the present invention, in an electrooptical device constituted by disposing a pixel matrix circuit, a driver circuit and a logic circuit on the same substrate, the pixel matrix circuit, the direr circuit and the logic circuit includes a plurality of TFTs each having an active layer of a crystalline silicon film and a subthreshold coefficient of 60 to 100 mV/decade, at least channel formation regions of the plurality of TFTs included in the respective circuits are made of a plurality of stripe-shaped crystalline regions, and respective atoms in the plurality of crystalline regions are continuously disposed without forming lattice defects in all or substantially all boundaries of adjacent crystalline regions in the inside of the plurality of stripe-shaped crystalline regions.
According to still another aspect of the present invention, in a method of manufacturing an electrooptical device comprising the steps of: forming an amorphous silicon film on a substrate having an insulating surface; selectively adding a catalytic element for promoting crystallization of the silicon film to the amorphous silicon film; forming a lateral growth region made of a crystalline silicon film by crystallizing the amorphous silicon film from the starting point of an added region of the catalytic element through heat treatment; forming an active layer in which at least a channel formation region is made of only the lateral growth region; forming a silicon oxide film on the active layer; and carrying out a heat treatment in an atmosphere containing a halogen element to remove the catalytic element in the active layer and to make thermal oxidation of the active layer, the step of adding the catalytic element is carried out by an ion implantation method or a plasma doping method, and at least one portion on the same substrate is added with the catalytic element with a concentration different from that of the catalytic element added to the other region.
According to still another aspect of the present invention, in a method of manufacturing an electrooptical device comprising the steps of: forming an amorphous silicon film on a substrate having an insulating surface; selectively adding a catalytic element for promoting crystallization of the silicon film to the amorphous silicon film; forming a lateral growth region made of a crystalline silicon film by crystallizing the amorphous silicon film from the starting point of an added region of the catalytic element through a heat treatment; forming an active layer in which at least a channel formation region is made of only the lateral growth region; forming a silicon oxide film on the active layer; and carrying out a heat treatment in an atmosphere containing a halogen element to remove the catalytic element in the active layer and to carry out thermal oxidation of the active layer, the step of adding the catalytic element is carried out by an ion implantation method or a plasma doping method, and the catalytic element with different concentration according to a channel length of the active layer is added to the same substrate.